Deposition of aluminum oxide by evaporative coating at atmospheric pressure (ECAP)

The Center for Plasma-Material Interaction (CPMI) has developed innovative coating method of evaporative coating at atmospheric pressure (ECAP). This new idea is an atmospheric-pressure-based process. Following the similar concept as the laser-assisted plasma coating at atmospheric pressure (LAPCAP) [1], the material captured by the plasma plume is atomic in nature (the evaporated metal atom) and should therefore end up deposited molecule-by-molecule as in a PVD fashion. By using the thermal energy from the microwave plasma, solid 99.99%+purity aluminum were evaporated and then produce a PVD-like alumina coating on a work piece. The aluminum target was inserted in the center of the microwave torch feeding a melt pool and evaporated into the surrounding plasma plume. A bottle neck was made in the antenna and could reduce the heat loss by 84%, thus allowing higher temperatures to exist in the sample-holder antenna tip. Gas shielding was used to keep the work gas pure. The film was deposited as Al₂O₃ using oxygen from the environment. Deposition rate was around 2μm/min. Gas flow rate around the antenna tip was about 0.9m/s, and the temperature of the plasma was about 1400°C at 1350W input power from simulations. Alpha and other metastable phases of aluminum oxide were found on the deposited films.